Question

In contrast to annelids the Platyhelminthes show
A. Radial symmetry
B. Presence of pseudocoel
C. Bilateral symmetry
D. Absence of body cavity

Answer 1

Hint: The Platyhelminthes exhibit bilateral symmetry. The body cavity is absent in Platyhelminthes. A pseudocoelom is present in Platyhelminthes. The fluid-filled body cavity which lies inside the external body wall of the organism is called pseudocoel. Any space or compartment in the body of an organism is called body activity.

Complete answer: Some animals possess a body cavity that is not lined by a mesoderm but the mesoderm is present as scattered pouches between the ectoderm and endoderm, such cavities are called pseudocoel and organisms that possess pseudocoel is called pseudocoelomates. Organisms that belong to the phylum Platyhelminthes possess pseudocoel. The radial symmetry is an organization in which organisms have similar parts arranged regularly around a central axis. Annelids don’t exhibit radial symmetry and also, Platyhelminthes don't exhibit radial symmetry. In an organism, if the opposite sides are similar then it is said to exhibit bilateral symmetry. Organisms belonging to the phylum Annelids exhibit bilateral symmetry. The organism that belongs to the phylum Platyhelminthes also exhibits bilateral symmetry. Cavities are potential spaces or a compartment that contains fluid. Platyhelminthes don't possess a body cavity. Platyhelminthes are divided into four classes, namely; Monogenea, Trematoda, Turbellaria and Cestoda.

Therefore, option (D) is the correct answer.

Note: Platyhelminthes are triploblastic, bilaterally symmetrical, dorsoventrally flattened, acoelomate flatworms with organ grade of construction without a definite anus, circulatory, skeletal or respiratory system. They have protonephridia as their excretory organ and are mostly parasitic with a few free-living.